Electroacoustic transducer

ABSTRACT

An electroacoustic transducer with a diaphragm strained to curvature and which is gripped at its edge regions with an elastic storage structure is described. The elastic storage structure adjoins an annular surface on at least one side. The inside diameter of the annular surface is larger than the inside diameter of the storage structure for the diaphragm.

United States Patent [191 Martin et a1.

[ ELECTROACOUSTIC TRANSDUCER [75] Inventors: Erwin Martin, Munich; Franz Beil,

Germering, both of Germany [73] Assignee: Siemens Aktiengesellschaft, Berlin and Munich, Germany [22] Filed: Apr. 18, 1972 [21] Appl. No.: 245,105

[30] Foreign Application Priority Data Apr. 23. 1971 Germany 2119911 [52] US. Cl. 179/115.5 ES, 179/180 51 Int. Cl ..H04r17/10 58 Field of Search 179/115.5 ES, 110 A, 180,

v179/179; 181/31 R, 33 D [56] I References Cited UNITED STATES PATENTS 3.206.558 9/1965 Shoot 179/110 A [4 1 Mar. 19, 1974 5/1930 Hayes 179/180 1/1960 Beaverson 179/110 A FOREIGN PATENTS OR APPLICATIONS 1.226,647 3/1965 Germany 179/110 A 1,961.217 6/1971 Germany 179/180 Primary Examiner-Kathleen H. Claffy Assistant Examiner-Douglas W. Olms 5 7 ABSTRACT 6 Claims, 3 Drawing Figures ELECTROACOUSTIC TRANSDUCER BACKGROUND OF THE INVENTION The invention described herein relates to an electroacoustic transducer of the type having a diaphragm strained to curvature. The diaphragm is gripped at its edge regions with a single or multiple storage structure of elastic material. The diaphragm contains in the transmission frequency band of the transducer, along with the resonant peak corresponding to the basic oscillation of the diaphragm, at least one resonant peak corresponding to a subharmonic oscillation of the diaphragm with an oscillation nodal line in the free portion of the diaphragm, in particular that one corresponding to the first subharmonic oscillation. Transducers of this type are generally used in telephones.

An object of the invention is to provide a means for correcting the oscillation condition of the diaphragm within the framework of the above mentioned frequency band in a simple manner, i.e., to adjust it such that a specific condition corresponding to the respective requirements is achieved.

SUMMARY OF THE INVENTION The foregoing and other objects are achieved according to the invention in that the storage structure serving to fasten and grip the diaphragm adjoins an annular surface on at least one side of the diaphragm. The inside diameter of the annular surface is larger than the inside diameter of the storage structure.

It has been shown that in this manner the fastening of the diaphragm can be influenced such that the frequency band of the transducer exhibits the desired characteristics. The fastening relationships can be regulated by the choice of the inside diameter of the support surface, such that with unchanged storage structure and unchanged diaphragm, very different oscillation conditions of the diaphragm can be set up. This yields the possibility of obtaining different oscillation conditions through possible corrections of the frequency of operation, which are adapted to the application at hand.

In accordance with the invention, the annular surface can be formed by a replaceable body placed in the transducer housing. Thus, it is made possible in a simple manner to adapt the oscillation condition to the required relationships, in that one can exchange'the body placed in the transducer housing with another body with another inside diameter.

It is advantageous for the construction of the transducer to form the annular surface from a flange-like extension of a body which is essentially disc-shaped and placed'parallel to the diaphragm. Such an arrangement permits further adjustment of the oscillation condition to be achieved in a simplemanner.

One can provide the disc-shaped body, for example, with at least one opening,'through which one can couple the volumes on either side of the body acoustically with each other, as desired.

The disc-shaped body can also contain at least one cavity, which is connected with the rear space of the diaphragm over at least one opening, whereby a Helmholtz resonator is formed.

It is possible to connect the cavity with the exterior space surrounding the body by at least one opening, whereby a'further possibility for influencing the acoustic condition of the transducer is formed.

BRIEF DESCRIPTION OF THE DRAWINGS The principles of the invention will be best understood by reference to a detailed description, given hereinbelow, of alternate preferred embodiments constructed according to these principles. These preferred embodiments are illustrated in the drawings in which:

FIG. 1 is a side sectional view of a piezo-electric microphone in which the storage structure for the diaphragm adjoins an annular surface, in accordance with the invention.

FIGS. 2 and 3 are side sectional views of two different variations of disc-shaped bodies, whose annular support surfaces are formed by a ring shaped flangelike extension of a disc.

DETAILED DESCRIPTION OF THE DRAWINGS The piezo-electric microphone shown in FIG. 1 has as its active element a diaphragm 2 provided with piezo-ceramic layer 1, which is held in a ring shaped elastic storage structure 3 of silicon rubber. Together with another ring 4 surrounding this storage structure 3, the components 3 and 4 adjoin a disc-shaped body 6 provided with a flange-like extension 5, which body has formed therein two openings 7 and 8. The disc 6 provided with flange-like extension 5 is made of insulating material. The flange-like member 5 forms an annular surface on which the elements 3 and 4 can rest. The arrangement shown thus is surrounded by a covering 9 and a housing 10, which extends into an insulating body 11 at its lower end. The insulating body 11 is penetrated by a center contact. The electrical connections have not been included in the drawing for the sake of clarity, but conventional electrical connections are used.

An essential characteristic of the invention is that the inside diameter pl'of the elastic storage structure is always smaller than the inside diameter p2 of the flangelike, annular extension 5 of the disc 6.

Using this construction, the oscillation condition of the diaphragm can be influenced in substantial measure, so that one can adjust the frequency of operation of the transducer, according to the requirements. Such adjustment can be made simply by inserting another body 6 having an extension 5 of different inner diameter.

F IG. 2 shows another version of a disc 13 with flan gelike extension 14, which has an inside diameter'p2. A cavity 15 is formed in the disc body, and this cavity is connected with the diaphragm rear space over an opening 16, so that a Helmholtz resonator is formed.

Likewise, a cavity 18 is placed in the disc 17 of FIG. 3, which here is connected withthe space surrounding it by two openings 19 and 20 through the opposite surfaces of the disc.

The foregoing description is intended only to be exemplary of the principles of the invention, and it is contemplated that the described embodiments can be changed or modified within the spirit-and scope of the appended claims.

We claim:

1. In an electroacoustic transducer structure having a diaphragm stressed by bending and gripped at its edge portions by agenerally ring-shaped storage structure constructed from elastic material, said diaphragm having a resonant peak at the desired frequency of operation of the transducerand at least one resonantpeak corresponding to a subharmonic of the frequency of operation with an isoillation nodal line in the free portion of the diaphragm, the improvement comprising:

support means having an annular surface, said storage structure adjoining said annualr surface,

said annular surface having an inner diameter greater than the inner diameter of said storage structure.

2. The electroacoustic transducer defined in claim 1 wherein said support means is constructed as to be removeable from said transducer structure.

3. The electroacoustic transducer defined in claim 1 wherein said support means is a disc-shaped member and wherein said annular surface is flange-like extension from a surface of said disc-shaped member.

4. The electroacoustic transducer defined in claim 3 said cavity. 

1. In an electroacoustic transducer structure having a diaphragm stressed by bending and gripped at its edge portions by a generally ring-shaped storage structure constructed from elastic material, said diaphragm having a resonant peak at the desired frequency of operation of the transducer and at least one resonant peak corresponding to a subharmonic of the frequency of operation with an isoillation nodal line in the free portion of the diaphragm, the improvement comprising: support means having an annular surface, said storage structure adjoining said annualr surface, said annular surface having an inner diameter greater than the inner diameter of said storage structure.
 2. The electroacoustic transducer defined in claim 1 wherein said support means is constructed as to be removeable from said transducer structure.
 3. The electroacoustic transducer defined in claim 1 wherein said support means is a disc-shaped member and wheRein said annular surface is flange-like extension from a surface of said disc-shaped member.
 4. The electroacoustic transducer defined in claim 3 wherein said disc-shaped member includes means defining an opening extending therethrough.
 5. The electroacoustic transducer defined in claim 3 wherein said disc-shaped member includes means defining a cavity enclosed in said disc-shaped member and means defining an opening through a surface of said disc-shaped member adjacent said flange-like extension to said cavity.
 6. The electroacoustic transducer defined in claim 5 wherein said disc-shaped member includes means defining an opening through the surface of said disc-shaped member opposite said flange-like extension to said cavity. 